Section 18. In any case where the department is obligated to pay any sums in excess of the approved budget because of an arrearage incurred by the recipient, under any of the programs administered by the department, the department shall be reimbursed in a manner not inconsistent with the federal social security act by deducting the amount of said arrearage from future budget payments to the recipient over a predetermined period of time. Such deduction shall not exceed five per cent of the recipient’s total budget allowance.

In any case in which aid is provided for the purpose of purchasing furniture under chapter one hundred and seventeen or one hundred and eighteen to a family with an unemployed father or a father whose whereabouts is unknown, said father shall be liable for reimbursement to the department for the amount of such payment if he is subsequently found to be gainfully employed.